There are numerous methods for manufacturing gearwheels. In the case of chip-producing soft pre-machining one differentiates between hobbing, gear shaping, generating planing, and power skiving. Hobbing and power skiving are so-called continuous methods.
The power skiving method was revived some time ago. The foundations of this method are approximately 100 years old. In the case of power skiving, as shown in FIG. 1A, an axis intersection angle Σ between the axis of rotation R1 of the power skiving tool 10 (also referred to as a skiving wheel) and the axis of rotation R2 of the workpiece 20, which is not equal to zero. The resulting relative movement between the power skiving tool 10 and the workpiece 20 is a spiral movement, which can be decomposed into a rotation component (rotational component) and a thrust component (translational component). A cylindrical helical drive can be considered to be a drive-technology analogy, wherein the rotating component corresponds to the rolling and the thrust component corresponds to the sliding of the flanks. The greater the absolute value of the axis intersection angle Σ, the more the translational movement component required for the machining of the workpiece 20 increases. Specifically, it causes a movement component of the cutting of the power skiving tool 10 in the direction of the two flanks of the workpiece 20. In the case of power skiving, the sliding component of the meshing relative movement of the engaged gear wheels of the helical wheel equivalent gearing is utilized to execute the cutting movement. In the case of power skiving, only a slow axial advance sax in parallel to the axis of rotation R2 of the workpiece 20 is required and the so-called shaping movement is omitted, which is typical for gear shaping. Therefore, no reverse stroke movement also occurs during power skiving.
The cutting speed in the case of power skiving is directly influenced by the rotational speed of the power skiving tool 10 or the workpiece 20 and by the axis intersection angle Σ used of the axes of rotation R1 and R2. The respective rotational movements are identified here with ω1 and ω2. The axis intersection angle Σ and therefore the sliding component are to be selected so that an optimum cutting velocity is achieved for the machining of the material at given rotational speed.
The movement sequences and further details of a previously known power skiving method can be inferred from the above-mentioned schematic illustration in FIG. 1A. FIG. 1A shows the power skiving of external gear teeth on a cylindrical workpiece 20. The workpiece 20 and the tool 10 (a cylindrical power skiving tool 10 here) rotate in opposite directions, as can be seen in FIG. 1A, for example, on the basis of the angular velocities ω1 and ω2.
Further relative movements also take place. The above-mentioned axial advance sax is necessary to be able to machine the entire gear teeth width of the workpiece 20 using the tool 10. The axial advance causes a displacement of the tool 10 in relation to the workpiece 20 in the parallel direction to the axis of rotation R2 of the workpiece 20. The direction of this movement of the tool 10 is identified in FIG. 1A with sax. If helical gear teeth are desired on the workpiece 20 (i.e., β2≠0), a differential advance sD is superimposed on the axial advance sax, which, as shown in FIG. 1A, corresponds to an additional rotation of the workpiece 20 around its axis of rotation R2. The differential advance sD and the axial advance sax are adapted to one another at the design point such that the resulting advance of the tool 10 in relation to the workpiece 20 takes place in the direction of the tooth gap to be created. In addition, a radial advance srad can be used, for example, to influence the crowning of the gear teeth of the workpiece 20.
In the case of power skiving, the vector of the cutting velocity νc essentially results as the difference of the two velocity vectors ν1 and ν2, which are inclined to one another by the axis intersection angle Σ, of the axes of rotation R1, R2 of tool 10 and workpiece 20. ν1 is the velocity vector on the circumference of the tool 10 and ν2 is the velocity vector on the circumference of the workpiece 20. The cutting velocity νc of the power skiving process can be varied by the axis intersection angle Σ and the rotational speed in the helical wheel equivalent gearing. The relatively slow axial advance sax, as already mentioned, only has a small influence on the cutting velocity νc in the power skiving method, which can be neglected. The axial advance sax is therefore not considered in the vector diagram with the vectors ν1, ν2, and νc in FIG. 1A.
FIG. 1B shows the power skiving of external gear teeth of a workpiece 20 using a conical power skiving tool 10. FIG. 1B again shows the axis intersection angle Σ, the vector of the cutting velocity νc, the velocity vectors ν1 on the circumference of the tool 10 and ν2 on the circumference of the workpiece 20, and the angle of inclination β1 of the tool 10 and the angle of inclination β2 of the workpiece 20. The angle of inclination β2 is not equal to zero here. The tooth head of the tool 10 is identified with the reference sign 4 in FIG. 1B. The tooth face is identified in FIG. 1B with the reference sign 5. The two axes of rotation R1 and R2 do not intersect, but rather are arranged skewed in relation to one another. In a conical power skiving tool 10, the design point AP is typically selected on the shared perpendicular of the two axes of rotation R1 and R2, since tilting of the power skiving tool 10 to provide clearance angles is not necessary. The design point AP is coincident here with the so-called touch point BP. The pitch circles of the helical wheel equivalent gearing touch in this design point AP.
During the chip-generating production of gearwheels on the workpiece, respective face-side edges result in the transition regions of the two flanks to the face plane, which can sometimes be very sharp and clearly pronounced. These edges are typically chamfered in a separate method step. There are very differing approaches to bring about the chamfering of such edges during the manufacturing of gear teeth.
Process-related burrs sometimes also arise in the edge region, which are removed in a machining step by so-called deburring.
Chamfering and deburring are equivalent processes, since frequently, the movement sequences are identical or nearly identical. The tools also do not necessarily have to differ from one another. Therefore, chamfering is always referred to hereafter, wherein deburring is also subsumed under this designation herein.
Special tools are sometimes used for chamfering, which either must be chucked in a machine in a separate method step before such a tool is used, or a separate axis having a special tool for chamfering is provided in the machine. To be able to chamfer both the right and also the left flanks in the edge region, quite complex movement sequences (relative movements between tool and workpiece) are sometimes necessary. In addition, in the case of power skiving, a rotational direction reversal usually has to be performed after the left flanks have been chamfered using a tool, for example. The chamfering of the right flanks can then only be performed after the rotational direction reversal. Such a rotational direction reversal is time-consuming and results in longer processing times. In particular for mass production, however, it would be desirable to shorten the processing times.